1-2 bags of play sand from Home Depot (6 bucks), a good filter (x2 the Magnum HOT), some Instant Ocean (13 bucks) or equivalent salt mix and your good to go, IF your only looking to do fish. If your looking to do reef that's what it gets somewhat complex. I switched from fresh to salt (fish only) last month and it has not been too $ difficult (well minus the fish! LOL). I am not a big fan of running lights all day on my 75g, plus all the other gadgets you need, so I am avoiding reef for now. Not to say some day I might dabble in it. 
So far I have really enjoyed it. And the wife loves the fish. She was not a big fan of large and in charge cichlids and cats....she prefers the pretty stuff....lol
So far I have really enjoyed it. And the wife loves the fish. She was not a big fan of large and in charge cichlids and cats....she prefers the pretty stuff....lol